The Versatility and Safe Use of Knuckleboom Cranes in Tree Care

Photo 1: The author’s Effer knuckleboom crane, mounted behind the cab of the truck, reaches over a house. Photo courtesy of Mark Moeske.

In recent years, knuckleboom cranes have increased in popularity in the tree care industry. And for good reason. They can increase production. They can be customized to meet each individual company’s needs. They also can increase efficiency and safety on job sites. But they must be used properly to be safe.

In this article, we’ll take a look at the various features of knucklebooms and the pros and cons of each on the job.

Let’s start with the similarities between a knuckleboom and a standardboom truck, or hydraulic, crane. All types of cranes are used to lift pieces from the tree while performing tree-care or tree-removal operations. They can move trees or tree parts to landing zones up to 200-plus feet from the point of origin. Knuckleboom and standard-boom cranes both have rated weight capacities specifying what they can safely lift. Both types of cranes need to be used with trained and qualified individuals to be safe. I recommend everyone operating a crane be certified for that type of crane.

The key to safely working with any crane starts with the setup of the crane. The ground must be stable and the crane must be set up properly and used within its rated capacities and limits. Shock loading must be avoided while using any crane. The ANSI Z133 safety standards always should be followed for safe operation. More on site setup further on.

What size is best?

Once a decision has been made to purchase and use a knuckleboom, there are many factors to consider when designing and building your unit. What are the trees you work with most of the time? How tall are they, and what kind of obstacles are you working around? What does your typical job site look like? Do you have 100-foot-tall trees in back yards and do you have big or small landing zones in which to put the picks down? Are there electrical conductors nearby?

If you have a large crane and the ability to make big picks but are unable to set the large picks down easily, would you be better off with a smaller, less-expensive crane? A smaller crane will fit into more yards and other smaller areas. A larger crane is better for reaching trees farther away and in backyards. A large crane can give you the reach you need by taking smaller picks.

DOT regulations are an important factor. How many axles do you need? Larger trucks need more axles and can be harder on turf or driveways. If you plan to have a truck body to carry debris, be sure the truck is large enough to handle the weight within DOT regulations, which vary by state.

Photo 2: This PM 48.5 rear-mount crane has 98 feet of vertical reach and sports a Mecanil grapple saw. This unit is owned by Cranebrook Tree Service & Tree Farm, a 21-year TCIA member company based in Auburn, New York. Photo courtesy of Todd Brady, GrapplesawTrucks.com, LLC.

Crane setup

There are various mounting options for knuckleboom cranes. With the cab-mount setup, the knuckleboom is mounted behind the cab of the truck, with its center of rotation also behind the cab (Photo 1). With this type of crane, you can add a dump bed behind it and be able to load debris into the truck and then dump it without the need to move the crane when it is time to dump. Hook lifts are utilized to swap different bodies when needed. Flatbed, log bunks, chip boxes and tool bodies are all options with this setup. The limitation on this setup is a loss of reach over the rear of the truck, as well as the distance to the front bumper from the crane’s center of rotation to the front.

The rear-mount setup has the center of rotation at or near the rear of the truck (Photo 2). With this setup, you are able to optimize your reach (radius) by backing up closer to your obstacle (i.e., a house) or tree. You may, however, be farther from your landing zone when setting the picks down over the front of the truck. You still are able to have a body between the crane and the cab but may be limited on unloading it. It would need to be unloaded with the crane, or you may have a side dump installed.

A center-mount crane is mounted with the center of rotation between the cab and the rear. This is often done with larger cranes and limits what the rest of the truck can be used for.

Knuckleboom cranes fold up when not in use. This means you are able to use a shorter truck than other cranes that have a boom that is 16 feet or more in length when stowed. On most rear- or cab-mount cranes, the center of rotation is usually off- set to the left or right of the center line of the truck to allow room for the crane to be stowed. This becomes important during the site-setup process.

Photo 3: The ability to articulate the boom over center allows a knuckleboom to reach under obstacles. Photo courtesy of the author.

Knuckleboom cranes have two or more pivot points, which allows you to reach over objects with less boom needed. A straight-boom crane that has to reach over a two-story building will need to extend more boom sections to reach the same radius. Once it is boomed down close to the building, it will need to extend the boom to get more horizontal reach. A knuckleboom can boom down the outer boom or jib and then extend out with less boom to reach the same radius (Photo 1).

The ability to articulate the boom over center allows a knuckleboom to reach under obstacles (Photo 3). In this case, it is also safer not reaching over the wires. Reaching over the wires with a crane using a hoist line to attach the sling to the tree has more potential swing, which could contact the wires. Although knucklebooms can have a hoist line, using a sling to attach to the hook alone limits the potential swing to the length of the sling.

Knucklebooms are designed with much better capacities at lower boom angles than other cranes. Horizontal and negative boom angles are a functional design of these cranes (Photo 4).

Photo 4: Horizontal and negative boom angles are a functional design of knuckleboom cranes. Photo courtesy of the author.

Remote control

Knuckleboom cranes come equipped with a remote control for operation. They are also available with top-seat and tethered controls. The remote control allows the operator to find the best position from which to view the work being done and the crane. When working in proximity to electrical conductors, the operator can be closer to see the exact position of the boom in relation to the conductors. The same is true with houses, fences, etc. The operator can stand in a backyard while making a pick, where he/she might otherwise not be able to see the work if at a crane-mounted control (Photo 5).

Photo 5: The remote control allows the operator to find the best position from which to view the work being done and the crane. Here, Dan Voss operates Altec’s boom-mounted grapple saw with the unit’s remote controls. Photo courtesy of Altec.

There are some important safety practices when using a remote control. The operator should not move backward while operating the crane. Operators need to be aware of their surroundings to avoid tripping. Remotes can be and should be in the stop position when moving to avoid inadvertently activating a crane function. Operators need to be in a safe location to avoid being struck by falling debris, and they should never be under a suspended load. When not in use, the remote control should be either with the operator or in the truck to avoid damage or access by someone not authorized.

Attachments

There are many attachments available for knuckleboom cranes. They can be outfitted with a man basket, which allows for much greater maneuverability and reach in and around a tree than truck-mounted aerial lifts. For a smaller company, this can eliminate the need for a second truck. With the ability to articulate over center with multiple booms, you can reach under obstacles to get to your work. Hoist lines allow the crane to be used in a manner similar to straight-boom cranes, but with the previously mentioned versatility of articulating the boom over and under obstacles.

Grapples for loading wood and brush can be added, making it quicker and easier to load debris already on the ground, but with more reach than a traditional log truck.

The most recent addition to the attachments available is the grapple saw, which allows an operator to make cuts on the tree from the ground with no personnel in the tree. Grapple saws also can be used to hold the piece being cut without the need for someone attaching a sling while a cutter makes the cut. This makes the turnaround time between cuts much quicker, since a climber or bucket operator doesn’t need to move up and down between the cuts. When the piece is held by a grapple saw, it can be rotated and tilted to maneuver it more easily away from obstacles and into a landing zone.

Using the grapple saw to make the cuts on a dead tree while holding the piece allows all personnel to be away from the dead pieces being cut. Having the ability to not have a climber in a dead and unstable tree is a big advantage of the grapple saw. Using a grapple saw to remove the tree also can allow one person to safely remove a tree by himself or herself.

Image 1: A typical load chart for a knuckleboom with the three parts of the boom labeled. Reference point A and the boom beneath it are “up-and-over” diagrams. These will be the stronger positions for the boom typically. Following the line from A to B, the crane can safely lift 2,030 pounds in any position along that line. Using the same amount of boom length but positioning the jib straight with the outer and inner booms, the crane can move from B to C and safely lift 1,630 pounds. This chart also shows that the jib can articulate 25 degrees over center. Graphic courtesy of Todd Brady, GrapplesawTrucks.com, LLC.

All that said, there are many safety factors to consider when using a grapple saw. The weight of the saw must be deducted from the standard load chart when calculating weight capacities (Image 1). Smaller pieces must be taken when cutting with the saw. When taking picks with a sling, the weight is below the hook; i.e., no side-loading. When using a grapple saw, there is potential for side-loading if the limb is out to the side of the boom or if the center of gravity is above the boom when taking vertical picks. Taking too large a piece also can add potential shock loading to the crane, which, as mentioned previously, should always be avoided.

Buying and using a grapple saw is not a substitute for training and experience. Knowledge of tree species and weights is more important, in my opinion, when using a grapple saw. Understanding how the wood fibers will react when cut and where the center of gravity is on the piece being cut are essential to making proper cuts. Before making the cut, an operator needs to be sure where the path of the saw will be to avoid cutting a limb that is not in the grapple’s grasp. Grapple saws should not be used for finish-pruning cuts.

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Site setup

Site setup for a knuckleboom also has differences from other cranes. Most knucklebooms are designed with stabilizers as opposed to outriggers. The tires should remain in contact with the ground. You should strive to set the crane up level, but knucklebooms can be as much as 5 degrees out of level, according to manufacturers’ recommendations. If it is necessary to raise the tires off the ground to be within the 5 degrees, then dunnage should be placed between the tires and the ground so they are not suspended.

If the crane is not level, it is important to understand how the crane is affected. When the crane is out of level, the boom can be side-loaded when the side faces uphill or downhill. When the top and bottom of the boom are up or downhill, the radius can increase or potentially be over center too far when raised all the way. This is why it is important to set the crane up within the manufacturer’s specifications.

The stabilizers must be on solid ground or dunnage is needed. You also may need to put dunnage under the stabilizers to get enough height or dig into a hill so the stabilizer can be set properly to level the crane. Many knucklebooms have stabilizers that can tip up to go over a fence or wall and then tip back down for use. This is very useful in residential areas.

Where you set the crane up in relation to obstacles should be planned out. If you plan to reach over the side of the truck and have a vertical obstacle such as another tree, then positioning the truck with the center of rotation on the opposite side of the truck from the obstacle will allow a better clearance. If you need to reach under an obstacle such as wires, having the center of rotation closer to them allows for more articulation over center. If you do a lot of this type of work, then where your center of rotation is on the truck is an important decision when having it built.

Other considerations

Once the crane is set up, are you going to rig the tree with the crane or use a grapple saw? If you are using a climber, a proper tie-in point (TIP) needs to be used on the crane. There are many TIP variations. The most important thing is to be sure it does not interfere with or become compromised by the crane. The ability to articulate creates situations where the TIP could rub on the boom. This should be avoided. Once the TIP is selected, a climber can be lifted using two tie-ins, one of which can be a lanyard. Then you can proceed rigging the tree similar to other crane picks, avoiding shock loading and minimizing movement.

Conclusion

Knuckleboom cranes are very versatile tools for the tree care industry. They can be built with many variations to meet the needs of different companies. You must apply experience and knowledge to determine how a knuckleboom can make a job safer, easier and more efficient. The key to making a good decision is to do your research. Visit other people who are using them. And get properly trained.

Mark Moeske is president of Allmark Services, Inc., a 22-year TCIA member company based in Nassau, New York.

This article is based on a presentation on the same subject that he was part of at TCI EXPO 2018 in Charlotte, North Carolina. For that presentation, he joined Rick Yoos, owner of Yoos Tree Service, a 26-year TCIA member company based in Egg Harbor Township, New Jersey, and Benjamin P. Heller, owner/COO of Hiawatha Tree Services, an accredited, nine-year TCIA member company based in Minneapolis, Minnesota.

To listen to an audio recording of the entire presentation, go to this page in the digital version of this issue of TCI Magazine online, at www.tcia.org , under the Publications tab, and click here.

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